1. Field of the Invention
The present invention relates to an active-matrix-type display apparatus which uses light-emission elements, such as EL (electroluminescence) elements that emit light when driving current flows through an organic semiconductor film or LED (light-emitting diode) elements, and thin-film transistors (hereinafter referred to as “TFTs”) that control the light-emission operation of this light-emission element. More particularly, the present invention relates to layout optimization technology for improving the display characteristics thereof.
2. Description of Related Art
Active-matrix-type display apparatuses which use current-control-type light-emission elements, such as EL elements or LED elements, have been proposed. Since any of the light-emission elements used in this type of display apparatus may emit light by itself, unlike a liquid-crystal display device, a backlight is not required, and there are advantages in that viewing angle dependence is small.
FIG. 22 shows, as an example of such a display apparatus, a block diagram of an active-matrix-type display apparatus which uses charge-injection-type organic thin-film EL elements. In a display apparatus 1A shown in this figure, formed on a transparent substrate are a plurality of scanning lines “gate”, a plurality of data lines “sig” extending in a direction intersecting the extension direction of these scanning lines “gate”, a plurality of common power-feed lines “com” which are parallel to these data lines “sig”, and pixels 7 corresponding to the intersections of the data lines “sig” and the scanning lines “gate”. With respect to the data lines “sig”, a data-side driving circuit 3 comprising a shift register, a level shifter, video in, and an analog switch is formed. With respect to the scanning lines, a scanning-side driving circuit 4 comprising a shift register and a level shifter is formed. Further, each of the pixels 7 is formed with a first TFT 20 in which a scanning signal is supplied to its gate electrode via the scanning lines, a holding capacitor “cap” for holding an image signal supplied from the data lines “sig” via this first TFT 20, a second TFT 30 in which an image signal held by this holding capacitor “cap” is supplied to its gate electrode, and light-emission elements 40 to which driving current flows from the common power-feed lines “com” when these are electrically connected to the common power-feed lines “com” via the second; TFT 30.
Specifically, as shown in FIGS. 23(A) and 23(B), in all the pixels 7, the first TFT 20 and the second TFT 30 are formed using two island-shaped semiconductor films, a relay electrode 35 is electrically connected to the source and drain regions of the second TFT 30 via a contact hole of a first interlayer insulation film 51, and a pixel electrode 41 is electrically connected to the relay electrode 35 via a contact hole of a second interlayer insulation film 52. On the side of the upper layers of this pixel electrode 41, a positive-hole injection layer 42, an organic semiconductor film 43, and a counter electrode “op” are multilayered. Here, the counter electrode “op” is formed over a plurality of pixels 7 in such a manner as to extend across the data lines “sig” and the like. Further, the common power-feed lines “com” are electrically connected to the source and drain regions of the second TFT 30 via the contact hole.
In contrast, in the first TFT 20, a potential holding electrode “st” which is electrically connected to the source and drain regions is electrically connected to an extended portion 310 of a gate electrode 31. On the side of the lower layers thereof, a semiconductor film 400 opposes this extended portion 310 via a gate insulation film 50, and since this semiconductor film 400 is made to conduct by impurities introduced thereinto, this semiconductor film 400, together with the extended portion 310 and the gate insulation film 50, constitute the holding capacitor “cap”. Here, the common power-feed line “com” is electrically connected to the semiconductor film 400 via the contact hole of the first interlayer insulation film 51. Therefore, since the holding capacitor “cap” holds an image signal supplied from the data lines “sig” via the first TFT 20, even if the first TFT 20 is turned off, the gate electrode 31 of the second TFT 30 is held at a potential corresponding to the image signal. Therefore, since the driving current continues to flow to the light-emission element 40 from the common power-feed lines “com”, the light-emission element 40 continues to emit light.
However, in comparison with the liquid-crystal display apparatus, in the display apparatus 1A, there is a problem in that the display quality cannot be improved because the pixels 7 are narrower by an amount corresponding to the requirement of the second TFT 30 and the common power-feed lines “com”.